1. Field of the Invention
The present invention relates to a valve timing control device (hereafter, referred as a device) altering timing for the closing and opening of an exhaust valve or intake valve of an internal-combustion engine (hereafter, referred as an engine) with reference to any operating conditions.
2. Description of the Related Art
FIG. 1 is a lateral cross sectional view of an internal configuration of a related valve timing control device. FIG. 2 is a longitudinal cross sectional view of the internal configuration of the related valve timing control device shown in FIG. 1. In the drawings, a reference numeral 1 denotes a first rotor, which is coupled to a crankshaft (not shown) as an output shaft of the engine by way of chains (not shown) and is rotatable in synchronization with the crankshaft (not shown). The first rotor 1 is integrated with a sprocket 2, a case 3 and a cover 4 using a threaded member 5 such as bolts. The sprocket 2 is rotated integrally with the crankshaft (not shown). The case 3 has a plurality of shoes 3a projected inwardly from an inner periphery of the case 3 to constitute a plurality of hydraulic chambers. The hydraulic chambers are blocked with the cover 4.
A rotor (second rotor) 6 is rotated relative to the first rotor 1 and is disposed in the case 3. The rotor 6 is integrally fixed on one end of an intake camshaft (hereafter, referred simply as a camshaft 7), which relates to timing for the closing and opening of an intake valve (not shown), or an exhaust camshaft (hereafter, referred simply as a camshaft 7), which relates to timing for the closing and opening of an exhaust valve (not shown), using a threaded member (not shown) such as bolts. The rotor 6 includes a boss section 6a having a bearing section 6b, which allows insertion of the one end of the camshaft 7, and a plurality of vanes 6c projected outwardly from an outer periphery of the boss section 6a in a radial direction of the boss section 6a to partition the hydraulic chambers, which are constituted by the shoes 3a of the case 3, into an advanced side hydraulic chamber 8 and a retarded side hydraulic chamber 9. The advanced side hydraulic chamber 8 means a hydraulic chamber to which a hydraulic pressure is supplied in order to move relatively the rotor 6, which is located at a reference position with respect to the case 3 shown in FIG. 1, toward the advanced side (in a direction of arrow X1) when the first rotor 1 including the case 3 rotates in the direction of arrow X1 shown in FIG. 1. On the other hand, the retarded side hydraulic chamber 9 means a hydraulic chamber to which a hydraulic pressure is supplied in order to move relatively the rotor 6, which is located at the reference position with respect to the case 3 shown in FIG. 1, toward the retarded side (in a direction of arrow X2) when the first rotor 1 including the case 3 rotates in the direction of arrow X1 shown in FIG. 1.
A first oil path 10 is arranged in the sprocket 2 and supplies a hydraulic pressure derived from an oil pump (not shown) to the advanced side hydraulic chamber 8 through an oil control valve (not shown) and an advanced side oil path (not shown) in the camshaft 7. A second oil path 11 is arranged in the rotor 6 and supplies a hydraulic pressure derived from the oil pump (not shown) and so on to the retarded side hydraulic chamber 9 through a retarded side oil path (not shown) in the camshaft 7.
An accommodation hole 13 accommodating a locking pin 12, which controls a relative rotation of the case 3 and the rotor 6, is so arranged at one of the shoes 3a of the case 3 as to pierce the case 3 in the radial direction.
Here, when the engine is started without producing a hydraulic pressure in the device, the rotor 6 vibrates in rotational directions due to a load of a cam (not shown) which is fixed integrally at the camshaft 7. Due to the vibration, contact and separation between the rotor 6 and the case 3 are repeated, and accordingly a beat noise occurs. The locking pin 12 prevents the occurrence of such a beat noise. The locking pin 12 includes a frontal minor-diameter section 12a allowing insertion into an engagement hole described later, a rear major-diameter section 12b having an outer diameter larger than the frontal minor-diameter section 12a, and a recess 12c formed at a rear bottom of the rear major-diameter section 12b. 
The accommodation hole 13 includes a minor-diameter hole section 13a accommodating the frontal minor-diameter section 12a of the locking pin 12, and a major-diameter hole section 12b with an inner diameter larger than that of the minor-diameter hole section 13a, the section 12b accommodating the rear major-diameter section 12b of the locking pin 12. A passage-selectable valve 16 is arranged at a position, which is adjacent to the shoe 3a equipped with the accommodation hole 13, of an end of the sprocket 2 close to the case 3. The passage-selectable valve 16 selects the higher hydraulic pressure of the two different pressures in the advanced and retarded hydraulic chambers 8 and 9, and supplies the selected pressure to a hydraulic chamber 15 defined between a frontal end face of the rear major-diameter section 12b of the locking pin 12 and a frontal end face of the major-diameter hole section 13b of the accommodation hole 13 by way of a hydraulic pressure supply passage 14 to unlock an engagement (hereafter, referred as a locking relation) of the locking pin 12 with the engagement hole described later. An advanced side hydraulic partitioned passage 17 communicates between the passage-selectable valve 16 and the advanced side hydraulic chamber 8, and a retarded side hydraulic partitioned passage 18 communicates between the passage-selectable valve 16 and the retarded side hydraulic chamber 9.
A prevention holder 21 is press-fitted in an outer periphery (outermost section of the device) of the major-diameter section 13b of the accommodation hole 13. The prevention holder 21 prevents the locking pin 12 and a coil spring 20 biasing the locking pin 12 against the rotor 6 at all times from being ejected out of the outermost section of the device. The prevention holder 21 is fixed at an outer periphery of the major-diameter section 13b of the accommodation hole 13 using a prevention pin 22. A discharge hole 23 is formed at a central section of the prevention holder 21 and discharges a backward pressure, which is produced in the accommodation hole 13 when the locking pin 12 moves back, to outside of the device. Moreover, the coil spring 20 is arranged between the recess 12c of the locking pin 12 and the prevention holder 21.
On the other hand, an engagement hole 24 is formed inwardly at a position, where the engagement hole 24 allows insertion of the frontal minor-diameter section 12a of the locking pin 12 when the rotor 6 is located at the reference position (most retarded position in FIG. 1) with respect to the case 3, of an outer periphery of the boss section 6a of the rotor 6 in the radial direction.
Seal means 25 are disposed at frontal ends of the respective vanes 6c of the rotor 6, and make contact with an inner periphery of the case 3 corresponding to each vane 6c to prevent oil leaks through a boundary between the advanced and retarded hydraulic chambers 8 and 9.
Incidentally, with a general device, speaking of the related device, a seal means like the seal mean above is often disposed at each of frontal ends (section A in FIG. 1) of each shoe 3a, which is located inside each of frontal ends of the respective vanes 6c. With one device, the seal means disposed at the section A positioned inside the device are however decommissioned in order to reduce cost of parts and so on and to simplify the structure of device as in the case of the related device. The device is constructed on premises that an infinitesimal clearance defined between the frontal end (case-side sealing face) of the shoe of the case and the outer periphery (rotor-side sealing face) of the boss section of the rotor serves a function of sealing between the chambers 8 and 9.
By definition, the purpose of preventing the oil leaks through the boundary between the advanced and retarded side hydraulic chambers 8 and 9 is to prevent a responsibility of the device from reduction due to reduction of the hydraulic pressure in the hydraulic chambers with the oil leaks. However, there is a possibility that the reduction of hydraulic pressure in each hydraulic chamber occurs due to other facts. Speaking of the example as shown in FIG. 1, as the flowability of actuating oil is increased at an elevated temperature of the oil, the oil flow between the chambers 8 and 9 in a peripheral direction of arrow B through an axial-direction clearance (hereafter, referred as a side clearance). Here, the side clearance is defined between the sprocket 2 and the case 3 or the rotor 6 or between the cover 4 and the case 3 or the rotor 6. As a result, there is the possibility that the reduction of hydraulic pressure in each hydraulic chamber occurs.
JP-A-130119/2000 discloses one side face, which faces the side clearance, of the sprocket 2 or the cover 4 is made of materials having a high thermal coefficient of expansion. In such a case, the one side face of the sprocket 2 or the cover 4 expands at the elevated temperature of the actuating oil and prevents the hot oil from passing through the side clearance.
However, it is possible to prevent the flow, which is indicated by arrow B in FIG. 1, of oil passing through the side clearance and the spill of oil in a direction of arrow C using the threaded member 5 without providing with special configurations.
JP-A-227205/1998 also discloses a device having no seal means arranged at the section A shown in FIG. 1. With the valve timing control device, a groove extending in a peripheral direction is arranged at a sliding face, and a roller is arranged rotationally in the groove in the peripheral direction. As a result, there is the possibility of reducing a sliding resistance occurred between a case and a rotor.
However, the related valve timing control device has the configurations as described above. There are problems that parts count and costs cannot be reduced because the roller is used instead of decommissioned seal means.
Moreover, in any of the related valve timing control devices above, when an axis of the device rotates eccentrically or skews on rotation of the engine for example, contact between both sealing face-to-sealing faces occur to wear them. At this time, there are problems that reliability of the device and changes in performance (increasing the quantity of oil leaks) are incurred.
Accordingly, it is an object of the present invention to provide a valve timing control device allowing control of the quantity of oil leaks, which are derived from the section A arranged inside the device decommissioning the seal means, within acceptable limits and ensuring the reliability of operation.
In order to achieve the object of the present invention, we provide a valve timing control device, a first rotor moving rotationally in synchronization with a crankshaft of an internal-combustion engine and having a plurality of shoes formed at an inner periphery of the first rotor, forming a plurality of hydraulic chambers; a second rotor arranged rotationally in the first rotor with the first rotor, including a boss section fixed at an end face of a camshaft of the internal-combustion engine and a plurality of vanes arranged at an outer periphery of the boss section and partitioning the hydraulic chambers into advanced side hydraulic chambers and retarded side hydraulic chambers; a seal means arranged between an outer periphery of each vane of the second rotor and an inner periphery of the first rotor; and a between-sealing-faces clearance defined between a frontal end of each shoe of the first rotor and the outer periphery of the boss section of the second rotor corresponding to the frontal end of the shoe and accepting the quantity of oil leaks having no effect on the responsibility of the device as a maximum value. In this way, it is difficult for actuating oils to pass through the between-sealing-faces clearance due to viscous resistance of the oils when the temperature of oil in the internal-combustion engine is not so elevated, it is possible to prevent the hydraulic pressure in the hydraulic chambers from reducing. When viscosity of oils is reduced to increase the flowability of oils as the temperature of oils in the engine is increased, a small amount of oil having no effect on the responsibility of the device leak from one of the hydraulic chambers to the other through the clearance. Therefore, it is possible to ensure operating stability of the device without reducing extremely the hydraulic pressure in the hydraulic chambers.
With the above arrangement, the between-sealing-faces clearance may be so set as to be larger than the maximum bearing clearance defined between the camshaft and a bearing section of the device supporting rotationally the camshaft. In this way, when the axis of the device rotate eccentrically within the range of the bearing clearance due to rotation of the crankshaft and soon of the engine, it is possible for the bearing clearance to accommodate relative displacement between parts due to the eccentricity. Therefore, it is possible to prevent sealing faces from wearing without occurrence of the sealing face-to-sealing face contact, including the outer periphery of the boss section of the second rotor and the frontal end of each shoe of the first rotor. Therefore, it is possible to improve the reliability of the device.
With the above arrangement, it may further comprise at least one oil-accumulation groove arranged at any one or both of the outer periphery of the boss section of the second rotor and the frontal end of each shoe of the first rotor. In this way, it is possible to cause a loss of kinetic energy of oils due to contraction within the oil-accumulation groove. Therefore, it is possible to reduce the quantity of oil leaks without adding complicated structure for blocking the flow of oil between the hydraulic chambers.
With the above arrangement, it may further comprise a recess arranged at any one of the outer periphery of the boss section of the second rotor and the frontal end of each shoe of the first rotor, and a projection arranged at the other and allowing insertion of the projection into the recess. In this way, it is possible to lengthen oil passages of the actuating oil between the sealing faces. Therefore, it is possible to increase the resistance to the flow of oil between the sealing faces including the recess and the projection to reduce the quantity of oil leaks.